The metabolism of arylamines and nitroaromatics by selected microorganisms will be investigated. Particular emphasis will be given to the ability of individual microbial species to produce aromatic nitroso metabolites either by arylamine oxidation or by nitroaromatic reduction. The ultimate fate of nitroso metabolites that are produced by such microbial redox reactions will then be investigated by high pressure liquid chromatography methods. The conversion of such nitroso intermediary metabolites to aromatic hydroxamic acids is proposed to be a major metabolic route, particularly by algal species. It is the production of the nitroso metabolites, and particularly the hydroxamic acid metabolites that poses a serious threat to human health.